The present invention relates to pumps in general and, in particular, to a new and useful valveless dosing pump which utilizes hard press-fit rings positioned within the bore of a housing defining inlet and outlet spaces therebetween with the rings receiving a first or relatively fixed piston and a second or swing piston.
In a volumetric feed apparatus, equal volumes of one or more liquid or gaseous secondary media are added in equal time intervals to a primary current, which may consist of solid, liquid and/or gaseous substances. The admixture can be effected continuously or intermittently. In the intermittent method, the secondary media must be divided into equal volumes, and the latter must be fed in equal or defined time intervals. The feeding can be effected either by varying the filling volumes or the time intervals from admixture to admixture.
In the continuous method, the secondary current is measured with known flow measuring methods and fed. In intermittent volumetric feedings, which are necessary for dosing small quantities, positive displacement pumps have proven to be most effective.
A known plunger pump is produced with piston diameters of 3 mm to 100 mm diameter, so that displacement volumes of several cc per hour to several cubic meter per hour are achieved. As a rule, the volume can be adjusted continuously even in a working pump, by varying the piston stroke. This is done by shifting the fulcrum of a tipping lever which transmits the movement from the driving motor over an eccentric shaft, which has already been transformed by an eccentric shaft into a reciprocating movement, to the piston. The fulcrum is shifted so that the piston always moves up to a dead front center, which is constant for all settings. This dosing pump thus has the same clearance volume over the entire piston stroke range. The accuracy of the dosing depends substantially on this clearance volume, that is, on the residual volume in the front dead center position of the piston, which is no longer delivered. When this residual volume is large, the compressibility of the dosing medium to be delivered enters into the output, particularly at higher pressures. The output thus depends on the backpressure. The greater the clearance volume is relative to the stroke volume, the less favorable is the output.
Another difficulty can be seen in the valves on the suction and pressure side of the stroke volume, thus, directly at the inlet and outlet socket of the dead center space. With excessive pressure in the dosing medium on the supply side, an uncontrolled flow of the dosing medium, independent of the piston movement, may appear on the pressure side, when the valve is opened (See Hengstenberg-Sturm-Winkler "Messen und Regeln in der chemischen Technik", Spring 1974, p. 407 to 408).
In another known dosing pump for liquids, namely, the Bosch injection pump, a piston with a constant stroke is used. The pump contains no suction valve, but only a pressure valve on the outlet side of the medium to be dosed. The adjustment of the displacement volume and, hence, of the dosing, is effected by socalled oblique edge control, which permits continuous adjustment by turning the piston, thus causing a part of the cylinder contents above the piston end face to flow back into the suction chamber.
This dosing pump works as follows: During the downstroke of the piston, the liquid to be dosed flows through lateral bores into the cylinder. During the upstroke, the delivery starts after opening the pressure valve to the outlet side, as soon as the piston covers the two lateral bores. Delivery takes place, however, only until the oblique control edge, which terminates a lateral recess in the piston wall and is connected over a groove with the end face, slides over one of the lateral bores. The pressure in the cylinder, that is, the pressure chamber, then collapses immediately, the pressure valve closes, and the dosing liquid, displaced by the further piston stroke, returns over the groove and the oblique control edge to the suction chamber. This pump also depends, for its absolute output, on the compressibility of the liquid to be delivered and the pressure generated there due to an unavoidable clearance volume. The pressure valve may only be open when the over-pressure opens the valve by the stroke of the piston. An elevated over-pressure in the flow medium can lead to an unintended flow from the suction pressure side (Hengstenberg-Sturm-Winkler "Messen und Regeln in der chemischen Technik" , Springer 1964, 409-410).
A known valveless pump for delivering liquids has two pistons which are jointly guided in the bore of a cylinder. The two pistons are moved in the same direction in such a way that one piston regularly performs the full stroke movement, while the other piston only performs a part of the stroke by the driving mechanism, correspondingly pushed over a feed pipe. The difference in the stroke, together with the bore diameter of the cylinder, forms the displaced volume of the pump.
One piston is termed the fixed piston, and is secured, without axial play, on a slide which surrounds the cylinder in U-form, while the other piston acts as a swing piston over two collars at its end between which an axial stroke relative to the slide is possible. When the slide is moved back and forth, by a driver, in its longitudinal direction, the swing piston trails behind the movement of the slide and thus of the fixed piston connected with it, due to friction. It thus bears in one direction of motion on the end face of the fixed piston, while a cavity is formed between the end faces in the other direction of motion, which represents the displaced volume. The cavity is formed and disappears in the respective dead centers of the movement. The cylinders for the supply and discharge of the medium to be delivered are arranged there. By pushing a wedge between the inner collar of the swing piston and the slide to different levels, the axial stroke of the swing piston, and thus the delivery, can be reduced or stopped.
The pump provided for the delivery of liquids cannot be used for the delivery of gases. The friction between the cylinder and the piston will lead rapidly to wear and thus jeopardize the delivery. According to the invention, the materials used are very important. In addition, the braking of the motion of the swing piston, by gland-friction, is disadvantageous. The braking forces are not defined here, and they can be readily changed. The changes enter into the displaced volume (See German Patent No. 79,345).